The present invention relates to a multichannel laser radar and especially to an infrared imaging laser radar system for producing a 3-D image using a laser beam array transmitter and receiver.
An active near infrared imaging laser radar system of the type of the present invention provides capabilities for target tracking, guidance, and fire control systems by generating a high frame rate, high resolution, 3-D imagery in a compact, low power package. The system uses integrated photonic technologies and hybrid manufacturing processes to miniaturize a parallel multichannel optical receiver and range counter circuit. It also utilizes a modular high speed parallel multichannel optical receiver which includes receiving and range circuitry. The present parallel multichannel system is capable of performing a 3-D snapshot image with a single laser pulse not requiring scanning, even though a scanner is used in the basic system.
In recent years, significant advances have been made in the development of imaging laser radar systems for use as seekers in air-to-air and air-to-surface systems and the like. These include single channel raster-scanned diode laser rangefinders which generate high resolution target images. A single channel system can be raster-scanned to produce false color range images and gray scale intensity images of the objects being imaged. However, several minutes are required to collect each image and the system is not easily portable. The single channel system laser has a target recognition and classification algorithm added thereto.
More recently, work has begun on a compact multichannel system which can be carried aboard a remotely piloted vehicle and can generate and process laser radar imaging in real time. A multichannel receiver uses multiple avalanche photodetectors with individual transimpedance amplifiers, range counters, and reflectance circuits for each of the avalanche photodetector elements. The transmitter can use multiple laser diode arrays along with a high speed lens to produce a vertical fan of a plurality of individual laser beams spaced a small distance apart. The transmitter and receiver are aligned so that individual beams illuminate one corresponding avalanche photodetector element in the focal plane of the receiver lens to generate one multiple pixel column of the image. The transmitter and receiver scan horizontally with a rotating prism or mirror such that an image is formed which is 4.degree. in elevation by 10.degree. in azimuth. The frame rate is 30 Hz against cluttered arrays of ground targets, the multichannel system has obtained a high success rate and demonstrated the potential of an active infrared imaging laser radar system for short range autonomous guidance systems.
The present invention is a further development of a multichannel imaging laser radar system which utilizes parallel multichannel receivers including a plurality of multichannel optical receiver photonic hybrids or MORPHS, which are conveniently plugged into a compact motherboard and are connected with the received laser array through a plurality of optical waveguides to the plurality of MORPHS.
Active imaging laser radars form 3-dimensional images which can be processed to provide target identification and precision aimpoint definition in real time. Earlier raster-scanned and pushbroom-scanned 3-D imaging laser radar receivers required multiple laser pulses to assemble a complete 3-D image frame. Platform/target motion and atmospheric effects caused tearing and jitter in the assembled 3-D images, which complicated the subsequent image processing and necessitated the use of stabilized scanning systems. This invention deals with a parallel/multichannel imaging laser radar receiver (PMR) and uses an array of multichannel laser radar receivers to form single-pulse, 3-D laser radar images, thus eliminating the complex and costly scanning system, and enabling much higher frame rates (1 kHz). The PMR uses a multichannel optical receiver photonic hybrid (MORPH), a high performance 16-channel laser radar receiver module which uses an array of InGaAs avalanche photodiodes (APDs) for eyesafe operation (silicon APDs and PIN diode detectors are also supported). The MORPH provides high downrange resolution (3 inches), multihit (8 per channel) range data for each detector on a compact (less than 3.times.5 inches) circuit card. Optical flux is transferred from the receiver focal plane to each MORPH via a fiber optic ribbon cable. An array of MORPHs are plugged into a compact passive backplane, along with a single digital control card (DCC). The DCC, which is the same form factor as the MORPH, synchronizes the MORPHs and transfers the digital range information to the host processor over a parallel data interface cable. The system described here illustrates one approach to integrating and packaging high-density photonic arrays and their associated signal processing electronics to yield a compact, low power, scannerless, high performance imaging laser radar receiver, using existing technology.